Modern computing and display technologies have facilitated the development of virtual reality (“VR”), augmented reality (“AR”), and mixed reality (“MR”) systems, wherein digitally reproduced images or portions thereof are presented to a user in a manner wherein they seem to be, or may be perceived as, real. A virtual reality, or “VR”, scenario typically involves presentation of digital or virtual image information without transparency to other actual real-world visual input; an augmented reality, or “AR”, scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the user. A mixed reality, or “MR”, system also introduces simulated objects into a real-world environment, but these objects typically feature a greater degree of interactivity than in AR systems. The simulated elements can often times be interactive in real time. Accordingly, AR and MR scenarios involve presentation of digital or virtual image information with at least partial transparency to other actual real-world visual input. The human visual perception system is very complex, and producing an VR/AR/MR technology that facilitates a comfortable, natural-feeling, rich presentation of virtual image elements amongst other virtual or real-world imagery elements is challenging.
The visualization center of the brain gains valuable perception information from the motion of both eyes and components thereof relative to each other. Vergence movements (i.e., rolling movements of the pupils toward or away from each other to converge the lines of sight of the eyes to fixate upon an object at various distances) of the two eyes relative to each other are closely associated with focusing (or “accommodation”) of the lenses of the eyes. Under normal conditions, changing the focus of the lenses of the eyes, or accommodating the eyes, to focus upon an object at a different distance will automatically cause a matching change in vergence to the same distance, under a relationship known as the “accommodation-vergence reflex.” Likewise, a change in vergence will trigger a matching change in accommodation, under normal conditions. Working against this reflex, as do most conventional stereoscopic VR/AR/MR configurations, is known to produce eye fatigue, headaches, or other forms of discomfort in users.
Stereoscopic wearable glasses generally feature two displays for the left and right eyes that are configured to display images with slightly different element presentation such that a three-dimensional perspective is perceived by the human visual system. Such configurations have been found to be uncomfortable for many users due to a mismatch between vergence and accommodation (“vergence-accommodation conflict”) which must be overcome to perceive the images in three dimensions. Indeed, some users are not able to tolerate stereoscopic configurations. These limitations apply to VR/AR/MR systems. Accordingly, most conventional VR/AR/MR systems are not optimally suited for presenting a rich, binocular, three-dimensional experience in a manner that will be comfortable and maximally useful to the user, in part because prior systems fail to address some of the fundamental aspects of the human perception system, including the vergence-accommodation conflict.
Full VR/AR/MR systems must also be capable of displaying virtual digital content at various perceived positions and distances relative to the user. The design of VR/AR/MR systems also presents numerous other challenges, including the speed of the system in delivering virtual digital content, quality of virtual digital content, eye relief of the user (addressing the vergence-accommodation conflict), size and portability of the system, and other system and optical challenges.
One possible approach to address these problems (including the vergence-accommodation conflict) is to project images at multiple depth planes. To implement this type of system, one approach is to use a large number of optical elements (e.g., light sources, prisms, gratings, filters, scan-optics, beam-splitters, mirrors, half-mirrors, shutters, eye pieces, etc.) to project images at a sufficiently large number (e.g., six) of depth planes. The problem with this approach is that using a large number of components in this manner necessarily requires a larger form factor than is desirable, and limits the degree to which the system size can be reduced. The large number of optical elements in these systems also results in a longer optical path, over which the light and the information contained therein can be degraded. These design issues result in cumbersome systems which are also power intensive. The systems and methods described herein are configured to address these challenges by presenting a fixed-distance mixed reality optical system.